Since electronic devices have recently become more compact and slimmer, they have become easily carried. Such electronic devices are typically carried in pockets or by hands but may have a form of being worn by body parts or various structures. Electronic devices in a wearable form, that is, wearable electronic devices, may include a main body (for example, a processor, a display, or a memory) for performing original functions mainly and a wearing part (for example, a strap) protruding from the main body by a predetermined length and fixing the main body to a body part or various structures.
However, the wearable electronic devices are used in only one form. For example, a wearable electronic device in a band form (for example, a watch) is only worn by a wrist, an arm, or a head and used. Additionally, due to the natures of wearable electronic devices, a relatively small size of displays may be mounted thereon in comparison to other electronic devices. Accordingly, when a large display is required, an additional device is connected to an electronic device and used.